[amdx]

I installed a subwoofer amp, at the moment I am using the high level input
on the amp. That means I'm running wires from left and right speakers to the
amp input connector. So I have the rear speakers in parallel with the sub
amp inputs.
All works fine when the ignition is turned on, but when the motor is
started one of two things happens.
1) The volume goes way down on the sub woofer.
When #1 happens the rear speaker volume is also very low.
2) or the subwoofer starts a low frequency rumble.
Once the car is started I can disconnect the subwoofer input then plug it
back in and all works well again.
What do you think could be the problem?
Thanks, Mike

[Dave]

"amdx" wrote in message
...
I installed a subwoofer amp, at the moment I am using the high level input
on the amp. That means I'm running wires from left and right speakers to
the amp input connector. So I have the rear speakers in parallel with the
sub amp inputs.
All works fine when the ignition is turned on, but when the motor is
started one of two things happens.
1) The volume goes way down on the sub woofer.
When #1 happens the rear speaker volume is also very low.
2) or the subwoofer starts a low frequency rumble.
Once the car is started I can disconnect the subwoofer input then plug it
back in and all works well again.
What do you think could be the problem?
Thanks, Mike



The sub amp is probably a big draw on the battery. When logic components,
i.e. the IC's which control the subwoofer amp, get low voltage they can do
weird weird things. Try wiring the power source direct to the battery with
an in-line fuse on the (+), bypassing the car's electrical system entirely.
Or, realize that it's an issue, and don't turn it on until the car is
running. Or, buy a separate battery to run it and modify your charging
system with a battery isolator to properly charge the two parallel
batteries.

[amdx]

"Dave" wrote in message
news:kMDsj.21455$w57.3801@edtnps90...

"amdx" wrote in message
...
I installed a subwoofer amp, at the moment I am using the high level input
on the amp. That means I'm running wires from left and right speakers to
the amp input connector. So I have the rear speakers in parallel with the
sub amp inputs.
All works fine when the ignition is turned on, but when the motor is
started one of two things happens.
1) The volume goes way down on the sub woofer.
When #1 happens the rear speaker volume is also very low.
2) or the subwoofer starts a low frequency rumble.
Once the car is started I can disconnect the subwoofer input then plug it
back in and all works well again.
What do you think could be the problem?
Thanks, Mike



The sub amp is probably a big draw on the battery. When logic components,
i.e. the IC's which control the subwoofer amp, get low voltage they can do
weird weird things. Try wiring the power source direct to the battery
with an in-line fuse on the (+), bypassing the car's electrical system
entirely. Or, realize that it's an issue, and don't turn it on until the
car is running. Or, buy a separate battery to run it and modify your
charging system with a battery isolator to properly charge the two
parallel batteries.
The amp is hardwired to the battery, It has a remote input that gets a
signal from the radio when it it turned on. So even when starting the car
then tuning on the radio that energizes the amp the problem occurs.
Thanks, Mike

[Richard Crowley]

"amdx" wrote ...
The amp is hardwired to the battery, It has a remote input that gets a
signal from the radio when it it turned on. So even when starting the car
then tuning on the radio that energizes the amp the problem occurs.

But there are lots of different ways of "hardwiring".
Specific discussion of where to attach, what guage of
wire to use for the distance and current draw, those
extra mega-capacitors they use, etc. are the things that
are specifically discussed in car audio forums, and rarely
here.

You didn't even mention what the voltage supply at the
amplifier is with the engine off vs. running (much less
while cranking). If you can't put numbers to the problem,
you could be chasing it around for months.

[AZ Nomad]

On Tue, 12 Feb 2008 11:32:06 -0600, amdx wrote:
I installed a subwoofer amp, at the moment I am using the high level input
on the amp. That means I'm running wires from left and right speakers to the
amp input connector. So I have the rear speakers in parallel with the sub
amp inputs.
All works fine when the ignition is turned on, but when the motor is
started one of two things happens.
1) The volume goes way down on the sub woofer.
When #1 happens the rear speaker volume is also very low.
2) or the subwoofer starts a low frequency rumble.
Once the car is started I can disconnect the subwoofer input then plug it
back in and all works well again.

What do you think could be the problem?

Check the battery voltage at the amp between the amps + and - temrinals. You
may have a bad ground to the trunk. Also check the control line with a
meter. Try the RCA inputs of the sub w/ the line levels disconnnected --
drive it with a walkman/xpod and see what happens. That would let you isolate
the problem from the signal inputs.

[Kevin McMurtrie]

In article ,
"amdx" wrote:

I installed a subwoofer amp, at the moment I am using the high level input
on the amp. That means I'm running wires from left and right speakers to the
amp input connector. So I have the rear speakers in parallel with the sub
amp inputs.
All works fine when the ignition is turned on, but when the motor is
started one of two things happens.
1) The volume goes way down on the sub woofer.
When #1 happens the rear speaker volume is also very low.
2) or the subwoofer starts a low frequency rumble.
Once the car is started I can disconnect the subwoofer input then plug it
back in and all works well again.
What do you think could be the problem?
Thanks, Mike


My guess is that you're engaging a crowbar or clamp protector on the
sub's input. Case #1 would be both leads and case #2 would be one lead.

When you crank your engine, your headunit and sub preamp might be
running at completely different voltages for a moment. That could
trigger input overload protection. It remaining in overload mode sounds
like a total design screwup somewhere. See what happens if you put 4
Ohm resistors in line with all speaker leads to the sub.

Most car audio equipment is crap because people want it cheap.

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